PROSTATE-SPECIFIC ANTIGEN DENSITY IS NOT AN INDEPENDENT PREDICTOR OF RESPONSE FOR PROSTATE-CANCER TREATED BY CONFORMAL RADIOTHERAPY

Although prostate specific antigen (PSA) density appears to be an impo rtant discriminator between benign and malignant prostatic disease, co nflicting data exist concerning its prognostic value. The present stud y was undertaken to confirm whether PSA density represents a new progn ostic indicator of disease-free survival for prostate cancer treated w ith conformal radiotherapy. Between April 1989 and December 1992, 186 patients with organ confined prostate cancer were treated with definit ive irradiation according to previously published conformal guidelines . The PSA density was defined as the ratio of the pretreatment serum P SA (ng./ml.) to the prostate volume (mi.) as determined from treatment planning computerized tomography. The median PSA density was 0.15 wit h a range of 0.02 to 2.12. A statistically significant advantage in ac tuarial freedom from biochemical relapse was noted for patients with p retreatment PSA levels less than 15 ng./ml. when compared to those wit h higher pretreatment PSA levels (3-year freedom from biochemical rela pse 85% versus 28%, p<0.001). Also, patients with PSA density of 0.15 or less had statistically superior freedom from biochemical relapse co mpared to their counterparts with higher PSA density (3-year freedom f rom biochemical relapse 88% versus 28%, p<0.001). Ina multivariate ana lysis only the baseline PSA (p<0.002) and the Gleason score (p<0.002) emerged as significant predictors of prolonged freedom from biochemica l relapse. The PSA density had no impact on freedom from biochemical r elapse whether it was entered into this multivariate model as a contin uous or a dichotomous variable. In our data base baseline PSA levels r emain the most powerful independent discriminant of response to confor mal irradiation. PSA density is only a surrogate for baseline PSA leve ls and does not refine the ability to predict prolongation of freedom from biochemical relapse following conformal radiotherapy.